Vacuum line runs cause low reading?

[smoke]

Agreed.

[datzenmike]

Counting the links proves nothing. What governs cam timing is the relationship between the V and the line above it at TDC. It should be below the line or just a hair off to the right. The horizontal line is equivalent to 4 degrees of cam timing or almost half a sprocket tooth

[NC280z]

So I think I may have found what's causing the engine to run with low vacuum. I brought the engine up to TDC, according to the saw-tooth scale. Timing on cam gear is at 1, v is just right of the cam tower notch. Took the gear off, moved it to positions #2 and then #3, aligning the bright-links to the crank sprocket/cam position indicators each time. Moving the gear from 1 down to 3 appears to have shifted the v-notch more to the LEFT of the cam tower notch, according to the manual moving from #1 to #2 or #3 should move the v-notch RIGHT, correct? I also took the chain off, and just placed the sprocket at the different numbered marks, and it doesn't appear to move the notch much, if at all.

 

Could it be possible that this gear was manufactured incorrectly? It has 40 teeth, per the manual. However, the timing kit this came in also had a timing chain that was made incorrectly (like, 10 extra links) AND the timing chain tensioner block wasn't drilled to receive oil from the engine block, as the old one was (I'm still using the old tensioner block, with new spring/rubber). Not to mention that the gasket had extra material on it, and I had to grind down the metal frame of the chain guides to get them to mount correctly.

 

I'll post images as soon as I can (sorry in advance for the poor quality. If what Datzenmike is saying about the cam tower notch equaling 4 degrees of cam timing, the gear has to be off IMHO, because moving to #2 and #3 didn't move the cam gear notch anywhere near that distance.

[ggzilla]

Try it

[datzenmike]

The sprocket should be turning to the right or clockwise direction if going up in numbers..

 

 

L16 (maybe18s) come from the factory on #1. All L20Bs are on #2. Don't know about L24/26/28.

The teeth are 20 and 40 for the proper 2 to 1 turns of the crank.

 

A worn chain or a head that has been overly shaved adds slack causing the crank position to be ahead of the proper cam timing. This means the piston is even further up the cylinder before the intake closes. This is beneficial at very high RPMs but not at low speeds. More importantly, during the overlap time, the exhaust valve closes later on the down traveling piston on the intake stroke. If the exhaust and intake valves are open it's hard to keep vacuum in the intake

[NC280z]

  

 

 

 

Here's the cam sprocket, minus the chain, set at the #1 and #3 positions. Notice the cam sprocket V-notch in relation to the cam tower notch. Am I doing something wrong here, or is this gear messed up?

[NC280z]

Datzenmike, Smoke, or I'm Blue, any of you guys have an idea on if this cam gear might be messed up? I've ordered a new set of crank/cam gears from Beck Arnley. These gears are stock reproductions, with the same viewing windows and a V-cut in the gear, rather than the u-shaped cut on this one. If it turns out that this is the issue, I'll post the product information for the timing kit that included this messed-up chain/gear/tensioner, so fellow Datsun owners can avoid it.

[datzenmike]

The pics are blurry and I can't make out the cam thrust plate mark. (maybe just me)

 

 

After adjustment did you back the crank up and reset to TDC again to remove any chain slack?

[NC280z]

I did, and there wasn't a change in the notch position, at least from what I could see. If anything, with the chain on the sprocket and free of slack, it looked like the cam sprocket notch actually moved further back, which would retard the cam rather than advance it. But it could be my eyes playing tricks on me, because the amount of difference between #1 and #3 was so insignificant it didn't appear to have moved at all. 

 

In the pictures above the cam thrust plate notch is perfectly centered withing the sprocket v-notch in the #1 position, and again in the #3 position without having changed anything other than the sprocket position itself. Swapping between #1 #2 and #3 doesn't move the cam sprocket notch one way or the other. 

[datzenmike]

That's an after market sprocket I believe.

[NC280z]

So I think I may have found the issue. Comparing the new crankshaft sprocket to the old, it would appear that the one I was running had an incorrectly-cut keyway, causing the cam to run as though it were retarded. The new cam sprocket has a stock-style V cut for the cam timing, and at the #1 position the V is just right of the cam tower notch at TDC, just as the manual shows it. I may run the cam sprocket in the #2 position for good measure, to see if that might increase the vacuum at idle. Anyone think this might be a bad idea? I'm going to check the clearances before doing so, but I don't think I'd have an interference issue with 4' of advance.

 

Also, don't know if this would have any effect, but the old gears look like the teeth were a bit wider at the very tip, compared to the Beck/Arnley I'm using now.

[smoke]

Advancing it a little will just drop when your power comes on and goes off a few hundred rpm, not a big difference, you will be fine.

[NC280z]

So something else interesting of note. I've set the cam sprocket to run in the number 2 position using the Beck/Arnley (new) sprocket(s) (cam/crank), when I tried setting it to the number 3 position just to experiment there wasn't enough slack in the chain to set it on the cam dowel (chain has like 3 road miles on it). Using the old cam gear from the mystery-brand timing set, I can set it at any of the numbered positions with no issue, and no visible change in notch position or chain tension. Does this mean the sprocket I was originally using is messed up? I've verified that the engine is TDC, and I'm using the bright links on the crank/cam sprocket marks as mentioned in the FSM, and that the chain tensioner is correctly seated. 

[ggzilla]

It only means the tensioner isn't backed off all the way. Your old gears had a bit of wear on them it sounds like.

[Nuclear Water Boy]

Correct Road Warrior it sounds like the tensioner isn't backing off enough. With all new timing bits you should be able to use any of the cam sprocket holes. But remember the sprocket holes were designed to keep you cams timing when the cam chain starts to stretch and making noise you move it to the next hole and when that starts making noise move it again. If you really want some gaines get an adjustable cam sprocket from Motosport with the multiple holes not just three. Then if you have the cams spec sheet degree it in, mark the hole and go from there. I did this once many years ago and the butt dyno said nice #$%n job!!!

[datzenmike]

So something else interesting of note. I've set the cam sprocket to run in the number 2 position using the Beck/Arnley (new) sprocket(s) (cam/crank), when I tried setting it to the number 3 position just to experiment there wasn't enough slack in the chain to set it on the cam dowel

 

Simply grab the center of the cam (away from any lobes) and turn it with vice grips until the cam dowel lines up with the hole in the sprocket.

[NC280z]

So I've got the 280z running today, but it still has the same vacuum reading (around 10inHg) at idle, even with the cam advanced to the #2 sprocket position. I am at a complete loss as to why it still has such a low vacuum reading. I thought maybe the distributor vacuum switch might be connected incorrectly, disconnecting the electrical connectors to the switch bumped the vacuum up slightly, but as far as I can tell the vacuum lines for the dizzy are correct for a federal manual ( vacuum switch end near front connected to dizzy, rear side connected to 3-way connector).

 

Could a messed-up evap canister cause a vacuum leak? I did a smoke test, but given the filters/activated charcoal in the canister I'd guess that it would prevent any smoke from being visible.

 

The engine also has a noticeable stumble right off idle, but clears up at higher rpm's. I'm guessing it's my old TPS, I'm going to order a new one shortly if they're even available. Might also order a large amount of thermite, and just send the car up in a blaze of glory, because it has me at my wit's end.

[ggzilla]

Could a messed-up evap canister cause a vacuum leak?

Yes, any vacuum operated device can leak. So test it. Disconnect the two vacuum hoses and plug them. You can drive the car that way temporarily.

[ggzilla]

I did a smoke test, but given the filters/activated charcoal in the canister I'd guess that it would prevent any smoke from being visible.

Stop guessing. What kind of smoke test did you do, and did you follow the directions closely?

 

If you injected smoke around the engine, did the smoke get sucked into the canister?

 

Or if you revved the engine at idle, did any smoke come out the tailpipe?

 

Or another test is to remove the oil filler cap with engine idling and look for blowby. The canister should not affect this test, but the block breather system will.

[NC280z]

I described the smoke test in earlier posts. I used the Smoke-Pro system, and followed the directions fully. Only visible leak was at the BCDD, due to a torn diaphragm, which has since then been replaced. As for removing the oil filler cap, I can't do that with the engine idling because removing the cap kills the motor. Also, it would be probably impossible to discern blow-by from the normal pressurized engine oil. That, and the smoke test I did isn't the kind you do with the engine running, I don't know that there is such a test with the engine running. 

[ggzilla]

Good. The canister will not interfere with that type of smoke test.

[NC280z]

So I tried blocking off the lines that run to the evap canister, no increase/change in idle vacuum. I tried connecting the lines according to the non-federal manual diagram (just to see), again no change/increase in vacuum at idle. I also went and measured the lobe lift for the cam, and if I'm doing it right with my digital caliper, it has been ground by Delta to .300" lobe lift, which should translate to .444" valve lift if the rocker arm ratio for our cars is 1.48. I'm using Schneider springs/retainers, and using the stock lash pads which were refurbished along with the rocker arms by Delta Cams.

 

The vacuum is still a steady low 10", with very little needle shake. It's driving me absolutely crazy that I can't get the vacuum past 10", no matter what I try or troubleshoot. Even with 140psi compression in each cylinder, I should still get around 20" vacuum at idle, correct?  

[ggzilla]

Yes. Maybe you gauge is bad.

 

How's the engine run? Plenty of power?

[NC280z]

I've verified that the gauge works fine on my '08 Frontier. Right now there's a bad stumble right off idle, so much so that I can't drive it but I think it's a matter of adjusting the TPS (just bought a new one). It idles fine however, no issues starting either.

[smoke]

Just for the info...the cam lift (what you're measuring) does not have that much effect on your vacuum. Well, not as much as when it opens and closes the valves. I think at one point you said it idles pretty smooth though right?